Method and Device for Track Counting in Optical Recording Media

ABSTRACT

The invention relates to the identification of the direction of the relative movement between a scanning beam of an optical scanner and the tracks of optical storage media. Use is made of the fact that the amplitude of the component TW of a track error signal TE, said component being brought about by wobble of the tracks, is maximal in the track center and minimal in the region between the tracks. A signal TW is thus present which does not assume its maxima and minima across the scanning location x at the same places as the track error signal TE. The invention describes devices and methods for determining the movement direction DIR of the scanning beam from the phase shift between the two signals.

The invention relates to the control of devices for accessing opticalstorage media, specifically the identification of the direction of therelative movement between a scanning beam of an optical scanner and thetracks of an optical storage medium.

On prerecorded optical storage media, so-called ROM media such asCD-ROM, DVD-ROM or the future successors thereof, or on alreadyprerecorded media, so-called R/RW media such as CD-R/RW, DVD+R/RW orsuccessors, the direction of the relative movement between the spot ofthe scanning beam and the tracks of the medium can be detected byevaluation of a track error signal and also the envelopes of a datasignal. For this purpose, a track zero crossing signal and also a mirrorzero cross signal are formed by comparators. In accordance with FIG. 6,the track zero crossing signal TZC is generated by comparing the trackerror signal TE with zero. The track error signal TE itself can beformed in various ways, such as, by way of example, by means of theso-called push-pull method, the differential push-pull method or thethree-beam method. The track zero crossing signal TZC exhibits a changeor an edge whenever the center of the information track of the datacarrier, also called groove, or the center of the region between twotracks, also called the land, is reached.

The methods of the prior art often relate to the fact that there is adifference in contrast between groove and land. Moreover, many of thepreviously known solutions are based on the fact that either the opticalstorage medium is already prerecorded or the scanning system works withthree scanning beams.

A method for forming the mirror zero cross signal MZC makes use of thefact that the modulation of the data signal by the information-carryingdepressions—also referred to as pits—is greatest on track centers andthe lower envelope of the data signal exhibits a low value there inaccordance with a low reflection factor. In the center between twotracks, on the other hand, the modulation by the pits is small and thelower envelope has a higher value there in accordance with a higherreflection factor. In accordance with FIGS. 6 and 18, in order to detectthis, the lower envelope HFE is formed by peak value detection from theDC-coupled data signal HF formed from the sum of all the photodetectorsignals. The envelope signal HFE is fed to a comparator 2103 eitherdirectly or after passing through a low-pass filter, which comparatorcompares said signal with a threshold value VC and generates the binarymirror zero cross signal MZC therefrom. The signal diagram of FIG. 6shows the signals TE, HF, HFE, TZC and MZC and also the associatedstates of the state logic 2102—shown in FIG. 18—as functions of timeassuming uniform crossing of the tracks.

The mirror zero cross signal MZC can also be formed by means of alow-pass filter and a comparator. For this purpose, the summation signalof selected detectors is low-pass-filtered in order to suppress thehigh-frequency signal components of the stored information and to obtaina signal, the so-called mirror signal MIR, which is proportional to theaverage reflectivity. In the case of the types of optical storage mediamentioned, the average reflectivity differs between the written-togroove tracks and the land regions in between. A comparator thencompares the mirror signal MIR with a threshold value and thus generatesa mirror zero cross signal.

Depending on the movement direction of the scanning being relative tothe tracks of the storage medium, there is a phase shift of +90° or −90°between the track zero crossing signal and the mirror zero cross signal,which corresponds to one quarter of the track width. FIGS. 6 and 7reveal the direction in which the scanning beam or the spot moves inrelation to the surface of the optical storage medium. FIG. 7 shows thestate diagram of the state logic 2102 which is shown in FIG. 18 and bymeans of which the movement direction of the scanning beam can bedetermined from the signals TZC and MZC. Proceeding from an arbitrarilyassumed initial state C3, defined by the signal values TZC=0 and MZC=1,there follows either the state C1 given TZC=0 and MZC=0 or the state C2given TZC=1 and MZC=1. The transition to C1 or to C2 indicatesunambiguously the direction in which the scanning beam is movingrelative to the tracks.

FIG. 18 also shows, as a further possible variant, that the signals TZCand MZC can also be conditioned by a D-type flip-flop 2104 in such a waythat the crossed tracks can be counted in a direction-dependent mannerby means of an up-down counter 2101.

In order to be able to generate a mirror zero cross signal as describedabove, a data signal HF must necessarily be present, which is affordedas standard in the case of prewritten-to ROM media. Many of thepreviously known solutions for error-free track counting are thus basedon the fact that the optical storage medium must already be prerecorded.In the case of write once or write many optical storage media of the“−R” or “−RW” type, however, there may be regions which have not beenwritten to and whose scanning gives rise neither to a data signal nor toa reflection that differs between groove and land. The above-describedmethod for generating the mirror zero cross signal, and thus adetermination of direction based on this method, cannot be employed,therefore, in regions that have not been written to.

Methods based on a use of scanning systems having more than one scanningbeam have been proposed for the determination of direction in regionsthat have not been written to.

The invention is based on the object of enabling a direction-dependenttrack counting such that, on the one hand, only one scanning beam isrequired for this purpose and, on the other hand, the movement directionof the scanning beam relative to the tracks of the medium can bedetected even in regions of optical storage media that have not beenwritten to.

According to the invention, a wobble signal is determined, whichdescribes that component of the track error signal which is broughtabout by the wobble of the tracks. Use is made of the fact that theamplitude of said wobble signal is maximal in the track center andminimal in the region between two tracks. A signal is thus presentwhich—similarly to the MZC signal of the previously known methods—doesnot assume its maxima and minima above the scanning location at the sameplaces as the track error signal. The resulting phase shift of thewobble signal relative to the track error signal then indicates themovement direction of the scanning beam relative to the tracks. For thispurpose, it is possible to generate either a signal corresponding to themirror zero cross signal, or else a direction signal indicating themovement direction of a scanning beam relative to the tracks scanned byit. A prerequisite for the application of the invention is that thetracks of the optical storage medium are wobbled with respect to theirimaginary center.

According to the invention, for driving a track counting device in ascanning unit for optical recording media, a wobble signal is determinedfrom the difference between a lower and an upper envelope of a trackerror signal that has been high-pass-filtered with a first cutofffrequency; a track zero crossing signal is determined from a track errorsignal that has been low-pass-filtered with a second cutoff frequency;the wobble signal and the track zero crossing signal are jointlyevaluated to ascertain whether, in the event of the sign changes of oneof these two signals, the respective other signal has positive ornegative values; and drive signals that are used to drive a sequentiallogic—also referred to as “finite state machine” or “finiteautomaton”—for track counting are determined from the result of thejoint evaluation.

A device according to the invention for determining drive signals fordriving a track counting device comprises a high-pass filter with afirst cutoff frequency, at the input of which the track error signal ispresent, and the output signal of which is fed in parallel to twoenvelope rectifiers for the upper and lower envelopes; a differenceforming unit, to which the output signals of the upper and lowerenvelope rectifiers are fed; a low-pass filter with a second cutofffrequency, at the input of which the track error signal is present; andalso an evaluation unit, the input signals of which are formed from theoutput signals of the difference forming unit and the low-pass filter,and which continuously evaluates whether, in the event of the signchanges of one of its input signals, the respective other of its inputsignals has positive or negative values, and provides the drive signalstherefrom.

The arrangements and methods according to the invention make it possibleto identify, on optical storage media with wobbled tracks, in the eventof track jumps, the instantaneous direction of the track jump and thetype of track just crossed, groove or land. Such a direction-dependenttrack counting with groove/land identification is advantageous forreliable track jumping and also reliable closing of the track controlloop at the end of track jumps.

Since only a single scanning beam is evaluated according to theinvention, the advantage is afforded that a track counting realized bymeans of the invention is not dependent on different track widths ortrack spacings and therefore does not have to be adapted to theseeither. Scanners having only one scanning beam also have the advantageof a simple and light mechanical construction. Developments of theinvention advantageously enable a reliable generation of a directionsignal or a reliable identification of direction even in the cases wherethe wobble signal has an offset, disturbances or amplitude variations.They are described in the description and also in the dependent patentclaims.

A joint evaluation of the wobble signal and the track zero crossingsignal with a sample and hold of the product of these two signals hasthe advantage that momentary disturbances of the drive signals aresuppressed.

A joint evaluation with a temporal integration has the advantage thatinstantaneous disturbances that may be superposed on the wobble signaland influence the envelope thereof are averaged out.

If a clock signal and a direction signal are determined as drivesignals, this has the advantage that an up-down counter can be drivendirectly with these signals.

If a first signal, which changes its value precisely when the scanningbeam crosses the center of a track, and a second signal, which changesits value precisely when the scanning beam crosses the boundary betweentwo adjacent tracks, are determined as drive signals, this has theadvantage that the evaluation logic of previously known track countingmethods can be adopted.

If the evaluation means contain product forming means, the input signalsof which are formed from the output signals of the difference formingmeans and the low-pass filter means, and sample and hold means, to whichthe output signal of the product forming means is fed, this has theadvantage that momentary disturbances of the drive signals aresuppressed.

If the low-pass filter means contain phase shift means, and theevaluation means contain product forming means, to which the outputsignals of the difference forming means and the low-pass filter meansare fed, and integration means, to which the output signal of theproduct forming means is fed, it is advantageously possible to determinethe relative phase angle of the two input signals of the product formingmeans by simply examining the polarity of the output signal of theintegration means.

In one development of the invention, provision is made of data signalforming means, HF detection means and changeover means controlled by theoutput signal of the HF detection means, the signal forming means form adata signal from the sum of the signals of the photodetectors, the HFdetection means detect whether a usable data signal corresponding to awritten-to region of the recording medium is present, and the changeovermeans, when a usable data signal is present, change over the input ofthe high-pass filter means to the data signal. This has the advantagethat the same functional units can be used for track counting onwritten-to and nonwritten-to parts of the recording media, which keepsdown the hardware outlay and the current consumption.

If the envelope rectifying means for the upper envelope are deactivatedwhen a usable data signal is present, this has the advantage of a lowercurrent consumption.

If the determination of the track zero crossing signal contains ahigh-pass filtering for suppressing very low frequency components, thishas the advantage of suppressing disturbing DC offsets in the trackerror signal.

Exemplary embodiments of the invention are illustrated in the drawingsand are described in more detail below.

In the drawings,

FIG. 1 shows the block diagram of a first exemplary embodiment,

FIG. 2 shows the block diagram of a second exemplary embodiment,

FIG. 3A shows the block diagram of a third exemplary embodiment,

FIG. 3B shows the block diagram of a variant of the third exemplaryembodiment,

FIG. 4A shows the block diagram of a fourth exemplary embodiment,

FIG. 4B shows the block diagram of a variant of the fourth exemplaryembodiment,

FIG. 5A shows the block diagram of a fifth exemplary embodiment,

FIG. 5B shows the block diagram of a variant of the fifth exemplaryembodiment,

FIG. 6 shows signal diagrams of a method of the prior art for generatinga mirror zero cross signal,

FIG. 7 shows a state diagram,

FIG. 8 shows signal diagrams with respect to the exemplary embodiment ofFIG. 1,

FIG. 9 shows signal diagrams with respect to the exemplary embodiment ofFIG. 2,

FIG. 10 shows signal diagrams with respect to the exemplary embodimentsof FIGS. 3A and 3B,

FIG. 11 shows signal diagrams with respect to the exemplary embodimentsof FIGS. 4A and 4B,

FIG. 12 shows signal diagrams with respect to the exemplary embodimentsof FIGS. 5A and 5B,

FIG. 13 shows signal diagrams with respect to a sixth exemplaryembodiment,

FIG. 14 shows a block diagram of the exemplary embodiment with respectto FIG. 13,

FIG. 15 shows signal diagrams with respect to a seventh exemplaryembodiment,

FIG. 16 shows a block diagram of the exemplary embodiment with respectto FIG. 15,

FIG. 17 shows a block diagram of a further embodiment,

FIG. 18 shows a block diagram of an arrangement of the prior art forgenerating a mirror zero cross signal.

FIG. 1 shows that the wobble signal TW is obtained by evaluating thehigh-frequency component of the track error signal TE. The track errorsignal TE, for its part, is formed generally by combining the outputsignals of a photodetector in such a way that the signals of theleft-hand half of the detector and the signals of the right-hand half ofthe detector are subtracted from one another. The photodetector 105shown here has four light-sensitive areas 105A, 105B, 105C, 105D inorder additionally to enable an astigmatism focus error signal to beformed. A photodetector having only two light-sensitive areas, which isdivided into a left-hand half and a right-hand half, would be sufficientfor obtaining the wobble signal TW. In the case of the four-areaphotodetector 105 depicted in FIG. 1, this is effected by the additionof the signals corresponding to the areas 105A and 105D, and 105B and105C.

The resulting frequency of the wobble signal TW obtained from thewobbled tracks should have a value that is at a sufficiently high levelabove the interference signal spectrum of the track regulation. Thewobble frequency advantageously lies above 300 kHz, so that theinterference signal spectrum of the tracking control can be suppressedby means of suitable filter measures. Furthermore, the modulation of thewobbled tracks should at least have a magnitude such that the quotientof wobble amplitude when the track regulator is activated divided bytrack error amplitude in the event of track crossings has the value0.15. These criteria are fulfilled for example in the case of storagemedia corresponding to the DVD+R/RW standard.

The simplest exemplary embodiment according to the invention as shown inFIG. 1 evaluates the high-frequency component and the low-frequencysignal component of the track error signal TE separately. Thehigh-frequency component of the track error signal is largely caused bythe wobble of the tracks. In the lower signal path for the low-frequencysignal component, the track error signal TE firstly passes through alow-pass filter 102 and is subsequently binarized by a comparator 107,as a result of which the signal TZC is generated. In order to suppressdisturbing DC offsets, an AC coupling 106 may advantageously be effectedupstream of the comparator 107.

The wobble signal TW is separated from the track error signal TE bymeans of a high-pass filter 101. The upper and lower envelopes of theoutput signal of the high-pass filter are determined by means of twoenvelope detectors 103, 104, and the difference between the twoenvelopes, which is determined in a subtractor 108, represents theinstantaneous amplitude TWENV of the wobble signal TW.

The instantaneous amplitude TWENV is maximal in the track center andminimal in the region between two tracks. It is binarized by means of acomparator 109, thus giving rise to a signal ENVZC which, relative tothe track error signal, has phase relationships comparable to those ofthe MZC signal. A D-type flip-flop 110 makes it possible to generate adirection signal DIR from the signals TZC and ENVZC, which directionsignal can be used for direction-dependent track counting with anup-down counter 111. As an alternative, the signals TZC and ENVZC may beevaluated by means of a state logic 112 in accordance with the statediagram of FIG. 7.

FIG. 8 shows by way of example a signal diagram for the exemplaryembodiment of FIG. 1. The part designated by 8A schematically shows thearrangement of grooves G and lands L across the scanning location x foran optical storage medium. All subsequent parts of the figure showsignal profiles across the scanning location x. A relative movement ofthe scanning beam accordingly corresponds in the diagram to a reading ofthe depicted values from left to right or from right to left. This isidentified by the arrows on the horizontal axes that are designated by“x” or “−x”: the counting arrow designated by “x” corresponds to amovement toward the right, and the counting arrow designated by “−x”corresponds to a movement toward the left. For signal profiles whichonly occur in the event of a movement toward the left or right, only thecounting arrow designated by “−x” or “x” is specified foridentification. The same mode of representation holds true for allsubsequent figures with signal profiles.

Part 8B shows the track error signal TE downstream of the low-passfilter. The envelope of the wobble signal TW illustrated underneath inpart 8C exhibits an amplitude maximum at each center of the groove G andan amplitude minimum at center of the land L. Part 8D shows theAC-coupled output signal of the subtractor TWENV. Parts 8E and 8F showthe two binarized signals TZC and ENVZC. The edges of the signal TZC areshifted by −90° with respect to MZC in the event of a movement towardthe right, or shifted by +90° in the event of a movement toward theleft.

FIG. 2 shows an alternative exemplary embodiment, which uses an up-downcounter 204 and has a doubled resolution during track counting incomparison with the exemplary embodiment of FIG. 1. The first blocks ofthe respective signal paths correspond to those of FIG. 1. Theinstantaneous amplitude value of the wobble signal TWENV is rectified bymeans of a synchronous rectifier 201, the first input of which isconnected to the output signal TWENV of the subtractor 205 and thesecond input of which is connected to the track zero cross signal TZC.The rectified amplitude values are sampled by means of a sample&holdblock 202, which is controlled upon positive and negative edges of thesignal TZC. An edge detector 206 is provided for this purpose, whichgenerates a pulse whenever the signal TZC has an edge. The output signalADIR of the S&H block 202 is binarized by means of a comparator 203 andindicates the movement direction DIR of the scanning beam, while theoutput of the edge detector 206 is used as counting pulse for theup-down counter 204.

FIG. 9 shows the signal diagrams associated with FIG. 2 and illustratesthe function of the synchronous rectifier 201, of the edge detector 206and of the S&H block 202. The signals designated by 9A to 9E correspondto the signals designated by 8A to 8E in FIG. 8. 9F designates theoutput signal SRENV of the synchronous rectifier 201. Its input signalTWENV is left unchanged if TZC is “high” and is in each case inverted ifTZC is “low”. The position of the S&H control pulses PLSTZC that aregenerated by the edge detector and designated by 9G or 9H differs inaccordance with the movement direction.

If the scanning beam moves from left to right, in accordance with thesignal profile designated by 9G, then the sample pulses occur in eachcase before the signal SRENV makes a jump upward. The signal SRENVdesignated by 9F is in each case sampled at the positions identified byarrows and held until the next edge of TZC. The corresponding outputsignal of the S&H block ADIR is designated by 9I and assumes negativevalues −V corresponding to “low” for a movement from left to right. Thearrows at the top of the signal profile designated by 9F correspondinglyindicate the sampling positions of the S&H block 202 in the event of arelative movement from right to left. Accordingly, the output signalADIR—designated by 9J here—of the S&H block 202 will assume positivevalues +V corresponding to “high”. The values of +V and −V,respectively, depend on the amplitude of the signal TWENV and thus onthe difference between the two envelopes of the wobble signal TW. Asignal DIR can be obtained from the signal ADIR by means of a comparator203. The track counter 204 is incremented or decremented with each pulseof the signal PLSTZC in accordance with the direction specified by DIR.

FIG. 3 shows two variants 3A and 3B of an exemplary embodiment with animproved arrangement for evaluating the amplitude variation of thewobble signal for forming the direction signal DIR. Particularly in thecase of DVD+R/RW media, the amplitude of the wobble signal is relativelysmall and the difference between the amplitudes on groove and land islikewise very small. In comparison with FIG. 2, the synchronousrectifier 301 has connected downstream of it a further S&H block 302 andalso a subtractor 309, which determines the envelope difference in thesynchronous-rectified signal TWENV between two pulses of PLSTZC.

FIG. 3B shows a variant in which a comparator 306 is directly connecteddownstream of the subtractor 309, the output signal of said comparatorbeing sampled by a D-type flip-flop 307. The output of the D-typeflip-flop 307 then forms the direction signal DIR.

FIG. 10 shows the signal diagrams associated with FIG. 3A. As can beseen, a possible offset in the signal TWENV designated by 10D or avariation of the envelopes of the wobble signal TW designated by 10Cdoes not influence the direction identification. This is achieved inthat the first S&H block 302, on each edge of the TZC signal, takes asample of the synchronous-rectified signal SRENV designated by 10F andthen the difference between instantaneous value and sample is formedwithin the interval until the next edge of the TZC signal, which resultsin a signal S/H1 shown in the signal profiles designated by 10G and 10Hfor the two movement directions. It is evident that at the instant ofsampling, the difference at the output of the subtractor is zero and thevoltage profile 10H that then forms changes toward negative values for amovement toward the right, while it assumes positive values in the eventof a movement toward the left in accordance with 10G. Upon occurrence ofthe respective next edge of the TZC signal, in a manner controlled bythe sampling pulses PLSTZC designated by 10I and 10J, respectively, thefinal value of these voltage profiles is sampled by the second S&H block304 and held until the next sampling pulse.

The sampled signal ADIR is illustrated in a manner designated by 10K or10L depending on the movement direction. A direction signal DIR can bedetermined in a simple manner from the polarity of the voltage (+V or−V) by means of a comparator. The two signals DIR and PLSTZC can be usedto control an up-down counter 308, as illustrated in FIG. 3A.

Parts 11A to 11N of FIG. 10 show the voltage profiles associated withFIG. 3B; in this case, 11A to 11J correspond to 10A to 10J. The voltageprofiles designated by 11G and 11H, respectively, are present at theinput of the comparator 306. Since the voltage profiles in the exampledepicted have positive or negative values, depending on the movementdirection of the scanning beam, upon the occurrence of the pulses PLSTZCdesignated by 11I and 11J, the output of the comparator 306 at thesepositions is “low” for a movement toward the right and “high” for amovement toward the left. The acceptance points of the binary outputsignal of the comparator 306 by the D-type flip-flop 307 are indicatedby vertical arrows in the signal profiles designated by 11M and 11N. Theoutput of the D-type flip-flop 307 then permits a statement about themovement direction of the scanning beam and may be fed as directionsignal DIR to the up-down counter 308.

FIGS. 4A and 4B show two further variants of an exemplary embodimentaccording to the invention. What is new here is the introduction of a90° phase shifter 401 and an integrator 402. The advantage with the useof an integrator 402 is that instantaneous disturbances that may besuperposed on the wobble signal TW and influence the envelope TWENVthereof are averaged out by the integration over a half-cycle of thetrack error signal. The function of the two new blocks 401, 402 isexplained below with reference to the signal profiles shown in FIG. 11.The phase shifter 401 converts the track error signal TE into a signalTE1 delayed by 90°, which is used for forming a product with theenvelope difference TWENV.

FIG. 4B shows a variant of the exemplary embodiment in which,analogously to in FIG. 3B, a comparator 403 and a D-type flip-flop 404are connected downstream of the integrator 402.

FIG. 11 shows the voltage profiles associated with FIG. 4A. The signalsdesignated by 12E and 12F, respectively, have a phase shift by 90° withrespect to the track error signal TE 12B. Since the diagram is to beread from right to left for a movement direction toward the left, atemporal phase shift of the signal TE in this case corresponds to asignal profile TE1 12F shifted by 90° toward the left. The productTEMENV of the envelope difference TWENV and the phase-shifted trackerror signal is illustrated in the parts designated by 12F and 12G forthe two movement directions. The integrator 402 downstream of the analogmultiplier 405 has the special feature of a reset input by which it canbe reset to an initial value of zero. The reset function is triggered bypulsed output signals of an edge detector 406, the pulses of which aregenerated upon signal edges of the phase-shifted track error signal TE1.The pulses PLSTZC are designated by 12J and 12K. The resulting outputsignal INT of the integrator 402 exhibits the behavior designated by 12Hor 12I, depending on the movement direction. With each falling edge ofthe reset pulse, the integrator 402 is reset and begins a newintegration cycle. The profile of the integration is determined by thesign and the value of the area integrals of the signals TEMENV shown in12F and 12G, respectively. Before the integrator 402 is reset, theintegration value is sampled by an S&H block 407. The sampling takesplace upon a rising edge of the pulse signal PLSTZC. The sampled valuesS/H1 are illustrated as parts 12L and 12M. The sampling positions areindicated by vertical arrows. The polarity of the sampled signals isevaluated by means of a comparator 408 and produces the direction signalDIR.

Parts 13A to 130 of FIG. 11 show the voltage profiles of the variantshown in FIG. 4B; in this case, 13A to 13K correspond to 12A to 12K. Theoutput signal of the comparator 403 is sampled by the D-type flip-flop404 upon rising edges of the pulse signal PLSTZC and may be used asdirection signal DIR for an up-down counter 409.

FIGS. 5A and 5B show a further exemplary embodiment. In contrast to theblock 410 in FIGS. 4A and 4B, here a comparator 501, which binarizes thephase-shifted track error signal, is arranged upstream of the input ofthe multiplier 502. Accordingly, as in FIGS. 3A and 3B, the latter hasthe function of a synchronous rectifier, which in practice can berealized more simply than the analog multiplier 405 from FIG. 4.

FIG. 12 shows the voltage profiles with respect to FIG. 5A in its partsdesignated by 14A to 14P, and also the voltage profiles with respect toFIG. 5B in the parts designated by 15A to 15R. The signal names usedcorrespond to those in the figures already described above. TheAC-coupled envelope difference signal TWENV shown in part 14D of thefigure is either switched through by the synchronous rectifier 502 ifthe output signal TZC1 of the comparator 501 that is shown in part 14Fand 14H, respectively, is “high”, or else inverted if TZC1 is “low”.

FIG. 14 shows a further, particularly advantageous exemplary embodimentthat combines the advantageous properties of the abovementionedexemplary embodiments. An identification of the movement direction ispossible despite disturbances, offsets or amplitude variations possiblyoccurring in the wobble signal TW. This is achieved by the use of twoS&H blocks 1701, 1702 and also a resettable integrator 1703. The signalTWENV is converted into a signal SRENV by the synchronous rectifier 502.The synchronous rectifier 502 is controlled by the track crossing signalTZC1 shifted by 90°. The output signal SRENV of the synchronousrectifier 502 is sampled by a first S&H block 1701, which, for its part,is controlled by sampling pulses PLSTZC.

The instantaneous value of the signal SRENV and the held sample duringthe interval between two edges of the signal PLSTZC are subtracted fromone another by a subtractor 1704, which results in a signal S/H1. Anintegrator 1703 connected downstream of the subtractor integrates thissignal in each case for a sampling interval between two pulses ofPLSTZC. Despite disturbances possibly present in the wobble signal, thefinal value of the integration unambiguously indicates the relativemovement direction by means of its polarity. The final value of theintegration is sampled by a second S&H block 1702 controlled by PLSTZCpulses. A comparator 1705 identifies the polarity of the sampled signalsand forms the signal DIR, which is used for controlling an up-downcounter 409 for track counting. The variant with a D-type flip-flopshown in the previous exemplary embodiments is likewise possible here,but is not illustrated.

FIG. 13 shows the signal diagrams associated with FIG. 14. Part 16Cagain shows a wobble signal TW having in this case both a DC offset andvariations of the envelope amplitude. The resulting envelope differenceTWENV shown in part 16D represents this. Parts 16I and 16J show thesignal SRENV in the case of the two movement directions, and parts 16Fand 16H show the respectively associated track crossing signal TZC1shifted by 90°. Parts 16M and 16N of the figure show the sampling pulsesPLSTZC that control the first S&H block, and parts 16K and 16L show thesignal S/H1. It can be seen from parts 16K and 16L that, at the instantof sampling, the difference at the output of the subtractor is zero andthe voltage profile that then forms exhibits negative half-cycles in thecase of the movement toward the right as shown by way of example in 16K,while it exhibits positive half-cycles in the case of the movementtoward the left assumed in 16L. The integrator 1703 integrates the areashatched in gray in parts 16K and 16L, and parts 160 and 16P show thevoltage profile at the output of the integrator 1703. Parts 16Q and 16Rof the figure show the values sampled by the second S&H block 1702controlled by PLSTZC pulses.

FIG. 16 shows the block diagram of a further exemplary embodiment. Theenvelope difference TWENV of the wobble signal TW, on whichdisturbances, DC offset and amplitude variations are superposed, issampled by a first S&H block 1901, the sampling instants being definedby the signal PLSTZC, which is again derived from a track error signalTE1 phase-shifted by 90° by means of a comparator 1902, 1903. Theinstantaneous value of the signal TWENV and the held sample during theinterval between two edges of the signal PLSTZC are subtracted from oneanother by means of a subtractor 1904. Since no synchronous rectifier isprovided in this exemplary embodiment, the half-cycles at the output ofthe subtractor 1904 may have positive or negative polarity. Inaccordance with the relative movement, however, the half-cycles in eachcase start with the value zero, since sample and instantaneous value areidentical at the sample instant. An integrator 1905 connected downstreamof the subtractor integrates the difference between the last sample ofTWENV and its instantaneous value in each case for a sampling intervalbetween two pulses of PLSTZC. The integrator 1905 has a reset input thatensures that each integration begins with the value zero. A second S&Hblock 1906 in each case samples the final value of the integrationbefore a new integration is started. The signal sampled by the secondS&H block 1906 accordingly indicates the area and polarity of the signalat the output of the subtractor 1904 for each interval between theoccurrence of two pulses PLSTZC. The downstream comparator 1907binarizes the integrator signal, thereby forming a signal ENVZC having aphase shift of +90° r −90° with respect to the TZC signal. As alreadyexplained above with respect to the prior art, the signals TZC and ENVZCare particularly advantageously evaluated by a state logic in accordancewith FIG. 7.

FIG. 15 shows the abovementioned signals of the exemplary embodimentfrom FIG. 16. Part 18B shows the track error signal TE. Parts 18I and18J illustrate the signal S/H1 at the output of the subtractor 1904 forthe two movement directions, which signal is formed by sampling anddifference formation from the envelope difference signal TWENV shown in18D. The sampling is controlled by signal PLSTZC, which is formed by anedge detector 1903 and has pulses in each case on the edges of thesignal TZC1 delayed by 90°. PLSTZC also controls the resetting of theintegrator 1905, the output signal INT of which is sampled by the secondS&H block 1906 at the positions identified by arrows, thus resulting inthe signal S/H2 shown in parts 180 and 18P. The signal ENVZC shown inpart 18Q is formed by binarization by means of a comparator 1907. ENVZChas a phase shift of +90° or −90°, dependent on the relative movement ofthe scanning beam, with respect to the signal TZC shown in part 18R,which is formed by binarization from the track error signal TE.

FIG. 17 shows an arrangement by means of which the blocks described inthe previous block diagrams can also be used for forming the MZC signalfrom the data signal HF on regions of the optical storage medium thathave already been written to. For this purpose, a switch 2001 isconnected upstream of the envelope detector 101, 103, 104 and is used toselect the track error signal TE or the data signal HF for high-passfiltering and subsequent processing. The selection is effected forexample by means of an HF detector 2002, which controls the changeovercontact of the switch 2001. In the event of a data signal HF beingpresent, it is used for track counting. Otherwise, the track errorsignal is selected and the wobble signal is generated therefrom in orderto enable direction-dependent counting on non-prerecorded regions. Theupper envelope detector 103 may optionally be switched off during theselection of the data signal HF.

For obtaining the MZC signal from the data signal HF as well, thedetection in accordance with the exemplary embodiments described aboveaffords greater detection reliability or insensitivity to disturbancesin comparison with the prior art shown in FIG. 18.

1. A method for driving a track counting device in a scanning unit foroptical recording media in which data are stored in tracks and theposition of the tracks transversely with respect to the track directionis modulated in a manner dependent on the position along the track in apredetermined manner, the scanning unit focusing a scanning beam ontothe recording medium and evaluating the scanning beam reflected from therecording medium by means of a plurality of photodetector segmentsarranged adjacent, and deriving a track error signal from the differencebetween the signals of the left-hand photodetector segments in the trackdirection and the signals of the right-hand photodetector segments inthe track direction; comprising the steps of: determining a wobblesignal from the difference between a lower and an upper envelope of atrack error signal that has been high-pass-filtered with a first cutofffrequency; determining a track zero crossing signal from a track errorsignal that has been low-pass-filtered with a second cutoff frequency;jointly evaluating the wobble signal and the track zero crossing signalin such a away as to ascertain whether, in the event of the sign changesof one signal, the respective other signal has positive or negativevalues; determining, from the result of the joint evaluation, drivesignals that are used to drive a sequential logic for track counting. 2.The method as claimed in claim 1, the joint evaluation containing asample and hold of a signal determined by product formation from thewobble signal and the track zero crossing signal.
 3. The method asclaimed in claim 1, the determination of the track zero crossing signalcontaining a phase shift, and the joint evaluation containing a temporalintegration of a product of the wobble signal and the track zerocrossing signal.
 4. The method as claimed in claim 1, a clock signal anda direction signal being determined as drive signals.
 5. The method asclaimed in claim 1, a first signal, which changes its value preciselywhen the scanning beam crosses the center of a track, and a secondsignal, which changes its value precisely when the scanning beam crossesthe boundary between two adjacent tracks, being determined as drivesignals.
 6. A device for determining drive signals for driving a trackcounting device in a scanning unit for optical recording media in whichdata are stored in tracks and the position of the tracks transverselywith respect to the track direction is modulated in a manner dependenton the position along the track in a predetermined manner, the scanningunit focusing a scanning beam onto the recording medium and evaluatingthe scanning beam reflected from the recording medium by means of aplurality of photodetector segments arranged adjacent, and deriving atrack error signal from the difference between the signals of theleft-hand photodetector segments in the track direction and the signalsof the right-hand photodetector segments in the track direction;comprising: high-pass filter means with a first cutoff frequency, at theinput of which the track error signal is present, and the output signalof which is fed in parallel to envelope rectifying means for the upperand lower envelope; difference forming means, to which the outputsignals of the upper and lower envelope rectifying means are fed;low-pass filter means with a second cutoff frequency, at the input ofwhich the track error signal is present; evaluation means, the inputsignals of which are formed from the output signals of the differenceforming means and the low-pass filter means, set up such that evaluationis continuously effected to ascertain whether, in the event of the signchanges of one input signal, the respective other input signal haspositive or negative values, and that the drive signals are provided. 7.The device as claimed in claim 6, the evaluation means containingproduct forming means, to which the output signals of the differenceforming means and the low-pass filter means are fed, and sample and holdmeans, to which the output signal of the product forming means is fed.8. The device as claimed in claim 6, the low-pass filter meanscontaining phase shift means, and the evaluation means containingproduct forming means, to which the output signals of the differenceforming means and the low-pass filter means are fed, and integrationmeans, to which the output signal of the product forming means is fed.9. The device as claimed in claim 6, which additionally contains datasignal forming means, HF detection means and changeover means controlledby the output signal of the HF detection means, the data signal formingmeans forming a data signal from the sum of the signals of thephotodetectors, the HF detection means detecting whether a usable datasignal corresponding to a written-to region of the recording medium ispresent, and the changeover means, when a usable data signal is present,changing over the input of the high-pass filter means to the datasignal.
 10. The device as claimed in claim 9, the envelope rectifyingmeans for the upper envelope being deactivated when a usable data signalis present.
 11. The method as claimed in claim 1, the determination ofthe track zero crossing signal containing a high-pass filtering with athird cutoff frequency below the second cutoff frequency.